<template>
  <div>
    <input id="excel-upload-input" ref="excel-upload-input" type="file" accept=".xlsx, .xls" class="c-hide" @change="handkeFileChange">
    <div id="drop" @drop="handleDrop" @dragover="handleDragover" @dragenter="handleDragover">
      Drop excel file here or
      <el-button style="margin-left:16px;" size="mini" type="primary" @click="handleUpload">browse</el-button>
    </div>
  </div>
</template>

<script>
import XLSX from 'xlsx';

export default {
    data() {
        return {
            loading: false,
            excelData: {
                header: null,
                results: null
            }
        };
    },
    methods: {
        generateDate({ header, results }) {
            this.excelData.header = header;
            this.excelData.results = results;
            this.$emit('on-selected-file', this.excelData);
        },
        handleDrop(e) {
            e.stopPropagation();
            e.preventDefault();
            const files = e.dataTransfer.files;
            if (files.length !== 1) {
                this.$message.error('Only support uploading one file!');
                return;
            }
            const itemFile = files[0]; // only use files[0]
            this.readerData(itemFile);
            e.stopPropagation();
            e.preventDefault();
        },
        handleDragover(e) {
            e.stopPropagation();
            e.preventDefault();
            e.dataTransfer.dropEffect = 'copy';
        },
        handleUpload() {
            document.getElementById('excel-upload-input').click();
        },
        handkeFileChange(e) {
            const files = e.target.files;
            const itemFile = files[0]; // only use files[0]
            if (!itemFile) return;
            this.readerData(itemFile);
            this.$refs['excel-upload-input'].value = null; // fix can't select the same excel
        },
        readerData(itemFile) {
            const reader = new FileReader();
            reader.onload = e => {
                const data = e.target.result;
                const fixedData = this.fixdata(data);
                const workbook = XLSX.read(btoa(fixedData), { type: 'base64' });
                const firstSheetName = workbook.SheetNames[0];
                const worksheet = workbook.Sheets[firstSheetName];
                const header = this.get_header_row(worksheet);
                const results = XLSX.utils.sheet_to_json(worksheet);
                this.generateDate({ header, results });
            };
            reader.readAsArrayBuffer(itemFile);
        },
        fixdata(data) {
            let o = '';
            let l = 0;
            const w = 10240;
            for (; l < data.byteLength / w; ++l) o += String.fromCharCode.apply(null, new Uint8Array(data.slice(l * w, l * w + w)));
            o += String.fromCharCode.apply(null, new Uint8Array(data.slice(l * w)));
            return o;
        },
        get_header_row(sheet) {
            const headers = [];
            const range = XLSX.utils.decode_range(sheet['!ref']);
            let C;
            const R = range.s.r; /* start in the first row */
            for (C = range.s.c; C <= range.e.c; ++C) { /* walk every column in the range */
                let cell = sheet[XLSX.utils.encode_cell({ c: C, r: R })]; /* find the cell in the first row */
                let hdr = 'UNKNOWN ' + C; // <-- replace with your desired default
                if (cell && cell.t) hdr = XLSX.utils.format_cell(cell);
                headers.push(hdr);
            }
            return headers;
        }
    }
};
</script>

<style scoped>
#excel-upload-input{
  display: none;
  z-index: -9999;
}
#drop{
  border: 2px dashed #bbb;
  width: 600px;
  height: 160px;
  line-height: 160px;
  margin: 0 auto;
  font-size: 24px;
  border-radius: 5px;
  text-align: center;
  color: #bbb;
  position: relative;
}
</style>
